Lung cancer rates have recently surpassed breast cancer rates as the leading cause of death by cancer among women. Women smokers risk for developing cardiac disease now approaches that of men. Women report greater fear of weight gain following cessation then men. Some studies also suggest that women smokers may have lower cessation and higher relapse rates than men. Combined smoking cessation and weight control treatments have not been successful at decreasing weight gain or enhancing achievement of smoking cessation. Exercise offers a healthful alternative to smoking that may allay women's fear of postcessation weight gain. Exercise is incompatible with smoking, facilitates regulation of body weight, moderates mood changes, and aids in decreasing responses to stress. The proposed study will test the hypothesis that vigorous exercise training enhances the achievement and maintenance of smoking cessation in healthy adult women. The study is a randomized trial with 2 conditions: a) standard cognitive-behavioral smoking cessation plus vigorous exercise; and b) standard cessation with equal contact time. A sample of 180 subjects will be recruited, treated for 12 weeks and followed for 12 months. This design permits separation of the effects of exercise from the effects of frequent contact with staff and other subjects. Smoking cessation outcome (7 day point prevalence) will be validated by saliva cotinine. Exercise adherence will be validated by attendance at supervised sessions, and maximal exercise testing. Secondary analysis of selected additional smoking outcomes and relapse patterns will also be examined. Successful smoking cessation in women could significantly reduce chronic disease mortality in this group. Although intensive, this kind of program could have advantages over pharmacologic treatments and/or could be made more disseminable and cost-effective, but only if the initial results of this rigorous trial are promising.